氮化硅陶瓷高温摩擦学性能

本文研究热压氮化硅陶瓷与３Ｃｒ２Ｗ８Ｖ钢组成的销－盘摩擦副，在空气中非润滑条件下，４００～８００℃不同载荷（４９～３４３Ｎ）的摩擦磨损性能；测定了磨擦系数和Ｓｉ３Ｎ４销的磨损因子；通过对Ｓｉ３Ｎ４磨损面的ＳＥＭ形貌观察、Ｘ射线相结构分析，探讨了陶瓷销的磨损机理     

高科技纤维在摩擦制动材料中的应用

本文介绍了一些高科技纤维在聚俣物基摩擦材料中的使用情况，指出在摩擦材料中使用高科技纤维已成为摩擦材料的一个发展趋势，但需要大大提高高科技纤维的性价比和使用纤维混杂技术。     

Effects of carbon black on tribology of blends of poly(vinylidene fluoride) with irradiated and non-irradiated ultrahigh molecular weight polyethylene

Friction and wear resistance are two vital tribological properties of polymer-based materials but optimization of both is rarely attempted. We have investigated blends of 70 wt% poly(vinylidene fluoride) (PVDF)+30% ultra high molecular weight polyethylene, the latter either un-irradiated or else γ-irradiated. Each sample contained varying amounts of carbon black (CB) and also had a varied degree of crosslinking and irradiation dose. We have determined static and dynamic friction, scratch resistance, and sliding wear in multiple scratching tests. Effects of the irradiation dose and CB concentration have been quantified. The electric conductivity threshold is reflected in a drop of static friction; formation of a continuous phase of the lubricant affects tribology as well as electrical properties—both for irradiated and for un-irradiated samples. The scratch resistance as represented by the residual (healing) depth is affected by crosslinking, by the stage at which irradiation is applied (before or after blending) and by CB addition. Crosslinking by moderate amounts of irradiation provides shallower residual depths while higher doses cause adverse results. Similarly, the CB lubricant can either improve or worsen the scratch resistance. A combination of both approaches produces either better or else worse results than crosslinking alone. Lower friction seems accompanied by higher scratch resistance. A combination of a specific irradiation dose and an optimized CB concentration lowers the sliding wear significantly. Strain hardening in sliding wear determination takes place for all materials studied, irrespective of the extent or radiation-induced crosslinking and of the presence and concentration of carbon black.     

Characterisation of cut and chip behaviour for NR,SBR and BR compounds with an instrumented laboratory device

ABSTRACT

Understanding the cut and chip (CC) effect in rubber is important for successful product development for tires used in off-road or poor road conditions and for other demanding applications of rubber. This research describes a laboratory testing method for characterising the CC fracture behaviour of rubber using a device that controls and records multiple applied loads and displacements during cyclic impact to the surface of a solid rubber specimen to mimic and quantify the CC damage experienced by tire tread compounds. To study the capabilities of the instrument, three model compounds were studied that are based on carbon black reinforced compounds of common elastomers used in tire treads: natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). These polymers have well-established CC tendencies in field performance of tire treads, with NR exhibiting the best CC resistance followed by SBR and finally BR. The same trend was found with the rubber impact testing approach that allowed the CC behaviour to be quantified using a new physical parameter which is the CC propensity (P). The relative ranking for CC resistance for the three compounds followed the fatigue crack growth resistances of the materials but was exactly opposite to the ranking of DIN abrasion resistance. This provides evidence that CC damage from impact by mm-scale asperities and abrasion of rubber against μm-scale asperities exhibit distinct characteristics in rubber.     

Preparation and properties of microcapsule with EVA core‐PU shell structure

Microcapsule with poly(ethylene‐co‐vinylacetate) (EVA) core‐polyurethane (PU) shell structure was synthesized by interfacial polymerization in aqueous polyol dispersion with ethylene diamine as the chain extender of toluene diisocyanate in poly(vinyl alcohol) aqueous solution as the stabilizing agent. The effects of polyol constituent on the average particle size and distributions, morphologies, color strength, and friction fastness of core‐shell particles were investigated to design microcapsule. The friction fastness of printed fabrics with EVA core‐PU shell microcapsules became the increase to 4–5 grades. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 893–902, 2007     

The tribological behavior of micrometer and nanometer TiO2 particle‐filled poly(phthalazine ether sulfone ketone) composites

Micrometer and nanometer TiO₂ particle‐filled poly(phthalazine ether sulfone ketone) (PPESK) composites with various filler volume fractions from 0.5 to 7.5 vol % were prepared by heating compression molding. The friction and wear behaviors of the PPESK composites were evaluated using the block‐on‐ring test rig by sliding PPESK‐based composite blocks against a mild carbon steel ring under dry friction conditions. The wear debris and the worn surfaces of the PPESK composites filled with micrometer and nanometer TiO₂ particles were investigated by using a scanning electron microscope (SEM), while the structures of PPESK composites and wear debris were analyzed with IR spectra. Experimental results show that antiwear properties of the PPESK composites can be improved greatly by filling nanometer TiO₂ particles, and the friction coefficient decreases when the filler volume fraction is below 2.5%, but when the filler volume fraction is above 2.5% the friction coefficient increases gradually with increasing filler volume fraction. In the case of micrometer TiO₂ filler, wear rates increase with increasing filler volume fractions under identical test conditions, and the friction coefficients are less sensitive to the filler volume fraction. It was also found that the wear mechanism of micrometer TiO₂ particle‐filled PPESK is mainly severe adhesion and abrasive wear, while that of nanometer TiO₂ particle‐filled PPESK is mainly slight abrasive wear. In the former case, there are no transfer film formed on the surface of the counterpart steel, and wear debris are in the form of long and large ribbon. While in the latter case, the wear debris was granule and their size was about 10 μm. In case of 1 vol % nanometer TiO₂ particle‐filled PPESK composites, the transfer film was fairly thinner and smoother, and the transfer film provided better coverage on the surface of steel ring, while that of 7.5 vol % was thicker and discrete. These account for the different friction and wear behavior of micrometer and nanometer TiO₂ particle‐filled PPESK composite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 906–914, 2004     

环形截面柱形管中粘性流体的研究

对环形截面柱形管中粘性流体的稳流和非平稳流进行了研究,得到了速度和粘性应力分布的规律,并且提出了能量损失的计算方法.通过Nave-Stocks方程式和用Weber函数对它们积分,对非平稳流进行了研究.通过建立数学模型,得到在一般边界条件下的封闭解.当流体处于静止状态并且在t=0时,压力系数变化率在流体上产生作用,在通解的基础上得到对非平稳流的解.同时获得瞬时和平均速度、动能和能量损失的变化规律.通过数值计算,对瞬时和平均速度,动能和动能损失系数变化量,以及由于粘性应力而造成的一般能量损失实验结果图进行了绘制.     

Fabricated and friction test anisotropy material of ultrasonic motor

The twisters for composed of anisotropic material were designed and manufactured.And two kinds of directional-composites were made:one was fiber direction vertical with frictional interface and another was parallel with frictional interface and moving direction.By varying the proportions of epoxy resin and fiber and arranging the orientations of fiber,the composites anisotropy along longitudinal and circumferential were got.Using density measurement,the mass fraction of resin and fiber were calculated.According to composite meso-scopic mechanics,the elasticity constants of composite were analyzed and calculated.The composite different thicknesses were sliced,and attach to the rotor,then the load characteristics,no-load speed,stop load of ultrasonic motor(USM)were test.The output properties of USM with 0.6 mm thickness composite were superior.The effect of friction material on ultrasonic motor was analyzed.Elastic modulus,thickness and micro-morphology of material are main factors which affect characteristics of ultrasonic motor.     

压电双晶片型旋转精密驱动器动态特性和控制

提出了以自由端带有集中质量的悬臂式压电双晶片为驱动单元的新型冲击式旋转精密驱动器.制作了驱动器样机,建立了基于Lugre摩擦模型的驱动器动力学模型.对驱动器动态特性进行了仿真分析和实验对比研究.根据驱动器的动态特性,提出了冲击式压电双晶片型精密驱动器特定的定频调压控制方法.仿真分析结果和实验结果吻合较好,表明该动力学模型符合驱动器的动态特性,可用于对冲击式压电双晶片型旋转精密驱动器的理论分析.     

A comparative study of tribological properties between perfluoro and non-perfluoro alkylsilane self-assembled monolayers(SAMs)

The tribological properties of perfluoro and non-perfluoro alkylsilane molecular films were investigated and compared detailedly. Their surface properties were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle (CA) measurement. A ball-on-disk tribometer was used to study the frictional properties of these alkylsilane monolayers. The experimental results reveal that the alkylsilane molecular films are good candidates to decrease friction and they have good capability to endure rigorous shear forces. Perfluoro alkylsilane molecular films are bonded better with the Si substrate than the simple hydrocarbon ones. The effects of sliding velocity and normal load on friction coefficient are evident and the friction coefficient increases with the increase of the sliding velocity. However, friction coefficient decreases with the increase of normal load initially and then increases, indicating there exists a critical normal load for the load effect. Funded by the National Natural Science Foundation of China (No.50730007 and 50805086), the Foundation of Tsighua Basic Research, and the National Key Basic Research Program of China(No. 2007CB607604)